Solid-state laser, semiconductor laser, and gas laser capable of emitting ultraviolet radiation, visible light and infrared radiation, over a wavelength range of 300 nm to 1200 nm, have been becoming more readily available in larger output and smaller size, and these types of laser are very important as recording light sources in direct plate making process using digital data output from a computer or the like. Recording materials sensitive to these various lasers have been extensively studied, and a first category of typical examples includes materials on which images can be recorded with infrared lasers at a wavelength of 760 nm or more such as positive-working recording materials and negative-working recording materials susceptible to acid-catalyzed cross-linking and the like. A second category includes recording materials sensitive to ultraviolet or visible light lasers at 300 nm to 700 nm such as negative-working recording materials susceptible to radical polymerization.
On the other hand, conventional lithographic printing plate precursors (hereinafter also referred to as PS plates) required a step for dissolving non-image areas away using an aqueous strongly alkaline solution (developing step) after imagewise exposure, and further required a post-treatment step during which the printing plates bearing a developed image are washed with water, or treated with a rinsing solution containing a surfactant, or treated with a desensitizing solution containing gum arabic or a starch derivative. The necessity of these additional wet processes is a major problem with conventional PS plates. The first half (imagewise exposure) of a plate making process may be simplified by the digital processing described above, but the effect of simplification would be insufficient so far as the second half (developing step) is a complex wet process. Especially given that global environmental protection has recently drawn a great deal of interest from the whole industry, it would also be desirable to use a developer at a pH closer to the neutral range or to reduce liquid waste for the purpose of environmental protection. Specifically, it would be desirable that the wet post-treatment process be simplified or replaced by a dry process.
An approach for simplifying the process to solve these problems is a one-solution or one-bath method in which development and gumming take place at the same time. This is a simplified development process comprising imagewise exposing a printing plate precursor without subjecting it to a water pre-washing step, followed by removal of the protective layer, removal of non-image areas and gumming at the same time using one solution or one bath, and drying the resulting plate without subjecting it to a water post-washing step, and then transferring it to a printing step. Lithographic printing plate precursors suitable for such simplified development must have an image-recording layer soluble in non-strongly alkaline solutions because no water post-washing step is included, but also they must have a hydrophilic substrate surface to improve staining resistance of non-image areas.
Such lithographic printing plate precursors are known from patent document 1 and patent document 2.